Mobile information terminals typified by smartphones and tablet devices have been actively developed. Such mobile information terminals are required to be lightweight, compact, for example.
In recent years, wearable electronic devices (also referred to as wearable devices) especially have been under active development. Examples of wearable devices include a watch-type device worn on an arm, a glasses-like device worn on a head, and a necklace-type device worn on a neck. For example, a watch-type device includes a small-sized display instead of a conventional watch dial to provide the user with various information in addition to the time. Such wearable devices have attracted attention to the medical use, the use for self-health management, or the like and have been increasingly put into practical use.
Mobile devices include secondary batteries that are capable of being repeatedly charged and discharged, in many cases. Wearable devices particularly include small-sized secondary batteries; thus, secondary batteries should be lightweight and compact and should be capable of being used for a long time.
For example, Patent Document 1 discloses a wearable device including a flexible secondary battery in which a film is used as its exterior body.